Engine may implement a strategy called selective catalytic reduction (SCR) to reduce engine emission in exhaust systems. SCR is a process where a gaseous or liquid reductant (e.g., ammonia, urea, etc.) is introduced into an exhaust conduit upstream of a catalyst. The SCR strategy converts NOx into N2 and water in the exhaust stream, reducing engine emissions and therefore the engine's impact on the environment. However, a number of factors can impact SCR performance. For example, decreased reductant injection atomization, caused by low pressure reductant injection, can negatively affect SCR operation. Reduced reductant evaporation, during cold starts for example, can also decrease NOx conversion in the catalyst. Incomplete flow mixing of the reductant and the exhaust gas can also decrease NOx conversion in the catalyst. In previous emission control systems a mixing device, downstream of a reductant injector, may be provided to improve SCR performance. However, the mixing device may be costly, bulky, and increase exhaust backpressure. Furthermore, mixing devices do not significantly improve reductant atomization and evaporation in the exhaust system. Thus, mixing devices may not enable the SCR catalyst to achieve desirable NOx conversion levels.
To address at least some of the aforementioned problems, an emission control system in an engine is provided. The emission control system includes a reductant injector extending into an exhaust conduit upstream of a catalyst, the reductant injector including a reductant passage receiving reductant from a reductant reservoir and a first exhaust gas inlet receiving exhaust gas from the exhaust conduit, a boundary of the first exhaust gas inlet at least partially delineated by an inlet wall extending into an interior exhaust passage from an outer housing surface, the interior exhaust passage adjacent to the reductant passage and receiving exhaust gas from the first exhaust gas inlet and fluidly separated from the reductant passage. The inlet wall in the aforementioned reductant injector can increase turbulence (e.g., swirl) of the exhaust gas flowing through and exiting the injector. Increased exhaust gas turbulence in the injector can increase the amount of heat transferred from the exhaust gas to the reductant. Increased reductant temperature increases reductant vaporization once the reductant is injected. Resultingly, conversion in the downstream catalyst can be increased to reduce emissions. Additionally, increased exhaust gas turbulence within the injector can promote mixing of the reductant stream and the exhaust gas stream exiting the injector, further increasing catalyst conversion to reduce emissions. Arranging the inlet wall inwardly from the injector housing also enables the profile of the injector to be reduced to increase the injector's compactness. Increased reductant injector compactness enables exhaust gas back pressure in the exhaust system to be reduced and simplifies reductant injector installation during manufacturing.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.